Surviving Lightning Strikes - How??

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Lmeagles36

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Ok all your electrical gurus. I am curious as to how soo many people survive lightning strikes? I understand simplified electrical equations and according to the math, about 100% of people should die if they get anywhere near lightning. If we are talking a bolt of lightning being somewhere in the 300,000 to 1 million volt range, someone's body having roughly 1,000 ohms of resistance at any given time due to rain, sweat, humidity, etc. and the human heart being able to only withstand about 100 mA before skipping a beat or stopping all together, then how does 300,000ish volts (figuring low), divided by 1,000 ohms = 300 amps going across someone's heart or through there body in general and doesn't blow apart everything in it's path to earth ground?

I know the current can go around a person's body and not necessarily through it, but if electricity takes all paths, and the human body is "a path" then even if a tiny fraction of that 300 amps I previously discussed went through the body instead of around it such as 1/300th of that current, it would still be 1 full amp which should still kill the body.

I understand either my logic or math is way off but I don't see where or how, otherwise people wouldn't have a 90 some % rate of surviving a lightning strike.
Bring on the education please!!! Thanks.
 
I'm no expert but here are somethings to consider...

- The 300,000-1million volt number is probably in reference to the potential difference between the cloud and the point where it strikes the ground. Once the lightning bolt strikes the ground, a gradient develops between the spot of the strike and the surrounding area. Assuming a uniform resistance through the earth, the amount of current flowing reduces as a cubic function of distance. In other words, as you get farther away from the strike, the amount of current flowing reduces rapidly. To make some back of the envelop calcuations: Take a medium soil resistivity of 500ohm, at your 300,000 volts, that's 600amps through a theoretical point where the lightning strikes. Now imagine a half-sphere beneath that point in level ground, 10ft in radius. The surface area of that half sphere is 628 square ft. Which means that if the current spreads out equally in all directions, at 10ft away you have less than 1amp flowing per square foot. It doesn't take much distance to drastically reduce the amount of current flowing.

- If someone is standing on the earth and not touching anything above them, then their torso, where the heart is, isn't particularly likely to serve as a path. There may be a potential difference between their two feet, but not so much between their legs and their head.

- I don't think many people survive a direct lightning strike. When you talk about a 90% rate of people surviving, I gather you are talking about people were nearby enough to be injured by a fork of electricity or flying objects caused by the strike. Perhaps also people in cars who are generally quite protected by relatively insulating materials in auto interiors these days, and so on. You have to define your criteria precisely to put a meaningful number on something like this.
 
Lmeagles36 said:
Ok all your electrical gurus. I am curious as to how soo many people survive lightning strikes? I understand simplified electrical equations and according to the math, about 100% of people should die if they get anywhere near lightning. If we are talking a bolt of lightning being somewhere in the 300,000 to 1 million volt range, someone's body having roughly 1,000 ohms of resistance at any given time due to rain, sweat, humidity, etc. and the human heart being able to only withstand about 100 mA before skipping a beat or stopping all together, then how does 300,000ish volts (figuring low), divided by 1,000 ohms = 300 amps going across someone's heart or through there body in general and doesn't blow apart everything in it's path to earth ground?

I know the current can go around a person's body and not necessarily through it, but if electricity takes all paths, and the human body is "a path" then even if a tiny fraction of that 300 amps I previously discussed went through the body instead of around it such as 1/300th of that current, it would still be 1 full amp which should still kill the body.

I understand either my logic or math is way off but I don't see where or how, otherwise people wouldn't have a 90 some % rate of surviving a lightning strike.
Bring on the education please!!! Thanks.
Click to expand...

The best simplest answer is here

VVVVVVVVVVVVV

petersonra said:
doesn't matter much how much electricity goes thru the body so much as how much goes thru your heart or other sensitive organ.
Click to expand...

Its all about the path the current associated with a strike takes in relation to someones body. You can see the path by looking at the injuries people get- they might have a severe burn on a part of their body for the entry wound and be missing a foot or hand, arm (whatever provided the shortest path to ground) etc where the juice exited, but as long as it stayed away from the heart or brain, they do live.

Its been speculated that a lot of people have survived a strike by wearing a necklace b/c the metal will shunt the current across the top of the body and down an arm and away from the heart.
 
The leader of the strike is not 1/2 Mv
The whole arc from the cloud the ground is
At the cloud is 1/2 mil, at earth approaching 0
so if the distance from cloud to earth is 3000'
v/ft is 500000/6000 = 85 v/ft (book value is 0.13 kv/m)
6 ft man sees ~ 500 v

if the strike has 20 ka Z = 500000/20000 = 25 Ohm
or 25/3000 = 8 mOhm/ft
so if the guy is 1000 Ohm the ionized cone around him will be much, much lower Z
so most of the current bypasses him
if he took 1/2 mil volts x 20 ka (10 Gw or 13.4 mil hp) he would be vaporized

that is why most lightening protection calcs use current, not voltage
eg, a strike hits a tower
the tower Z can be calculated based on geometry, etc
tables give the ka for strikes for different regions, probabilty based
knowing Z and i, v can be calculated
and suitable arrestors and insulators selected

the grad course's text I recently completed had a chapt on lighting
it was presented in order to select BIL
std wave and magnitude data from the book
 
jaggedben said:
I'm no expert but here are somethings to consider...

- The 300,000-1million volt number is probably in reference to the potential difference between the cloud and the point where it strikes the ground. Once the lightning bolt strikes the ground, a gradient develops between the spot of the strike and the surrounding area. Assuming a uniform resistance through the earth, the amount of current flowing reduces as a cubic function of distance. In other words, as you get farther away from the strike, the amount of current flowing reduces rapidly. To make some back of the envelop calcuations: Take a medium soil resistivity of 500ohm, at your 300,000 volts, that's 600amps through a theoretical point where the lightning strikes. Now imagine a half-sphere beneath that point in level ground, 10ft in radius. The surface area of that half sphere is 628 square ft. Which means that if the current spreads out equally in all directions, at 10ft away you have less than 1amp flowing per square foot. It doesn't take much distance to drastically reduce the amount of current flowing.

- If someone is standing on the earth and not touching anything above them, then their torso, where the heart is, isn't particularly likely to serve as a path. There may be a potential difference between their two feet, but not so much between their legs and their head.

- I don't think many people survive a direct lightning strike. When you talk about a 90% rate of people surviving, I gather you are talking about people were nearby enough to be injured by a fork of electricity or flying objects caused by the strike. Perhaps also people in cars who are generally quite protected by relatively insulating materials in auto interiors these days, and so on. You have to define your criteria precisely to put a meaningful number on something like this.
Click to expand...

Car strikes are often survived not because of insulation but because the frame/body tends to act as a Faraday cage. Stunt performers who mess with Tesla coils and millions of volts (as well as HV lineman) wear steel mesh suits to direct the electricity over rather than thru them.

Lightning is an odd phenomena; one Roy Sullivan survived a reported 7 strikes, yet 300+ reindeer got on Santa's bad list with one strike. Seen a few news stories with multiple people injured or killed from lightning hitting a metal fence.

Lightning's short duration probably also contributes to its survivability; coming into contact with MV/HV transmission lines seems much more lethal.
 
JFletcher said:
Car strikes are often survived not because of insulation but because the frame/body tends to act as a Faraday cage. Stunt performers who mess with Tesla coils and millions of volts (as well as HV lineman) wear steel mesh suits to direct the electricity over rather than thru them.
Click to expand...

Thanks for being precise about it.

Lightning is an odd phenomena; one Roy Sullivan survived a reported 7 strikes, yet 300+ reindeer got on Santa's bad list with one strike. Seen a few news stories with multiple people injured or killed from lightning hitting a metal fence.
...
Click to expand...

A difference between Roy and the reindeer is that Roy doesn't walk with his hands on the ground. See my second point in the post you quoted. Agreed that lightning is odd, though.
 
There are 2 factors that determine the severity of a shock
magnitude and time

BIL testing uses a 1.2/50 pulse
rises to 100% in 1.2 usec and decays to 50% in 50 usec
we'll ignore rise to simplify things and this is justified since it is so short

the decay can be modelled as
i = Ipeak x e^-(13900 x t)
25 usec 70%
50 usec 50%
75 usec 35%
100 usec 25%
200 usec 6%
300 usec 1.5%
400 usec <0.4%, call it 0

if we assume my previous 500 v (way too high) across a 1000 Ohm person
Ipeak= 500/1000 = 500 mA
from above it decays from 500 to 0 in 400 usec or 0.4 msec
essentially the duration
the peak is 500 but decays rapidly, avg is close to 200 (don't feel like integrating lol)
we'll use 300 mA to be conservative
For 0.4 msec

Dalziels equation for fibrillation
i mA = 175 (avg man) / sqrt(t sec)
or time = (175/300)^2 = 0.34 sec is survivable <<< 0.0004 sec
factor of 85

how much current can be survived per Dalziel in 0.0004 sec?
equation likely not valid at this small a time, but should give an order of magnitude
8750 mA (the person would never see that much) factor of 30
fibrillation would be the least of his worries
P = 8.75^2 x 1000 = 76 kw or 100 hp
v required = 8.75 x 1000 = 8750 v, not happening with lightening

now much depends on how well coupled to earth, golf spikes vs tennis shoes, etc
this will dampen the surge, lower peak and longer decay rate

it does not surprise me a high % survive
 
Last edited:
mike_kilroy said:
Sounds mighty safe then to stand under a tree during a lightening storm, huh?

Sent from my SM-G900V using Tapatalk
Click to expand...

1/mil odds
how many exposed?
500 hit
50 die
the chance of being hit is very small (with a large number exposed)
the chance of death 10 times less
auto deaths 32000
odds are better under the tree

90% survive, meaning the chance of survival is 10 times that of being killed
meaning the vast majority survive, in other words likely to survive because not enough current to kill you

According to the NOAA, over the last 20 years, the United States averaged 51 annual lightning strike fatalities, placing it in the second position, just behind floods for deadly weather. In the US, between 9% and 10% of those struck die, for an average of 40 to 50 deaths per year (28 in 2008).
 
Ingenieur said:
There are 2 factors that determine the severity of a shock
magnitude and time

BIL testing uses a 1.2/50 pulse
rises to 100% in 1.2 usec and decays to 50% in 50 usec
we'll ignore rise to simplify things and this is justified since it is so short

the decay can be modelled as
i = Ipeak x e^-(13900 x t)
25 usec 70%
50 usec 50%
75 usec 35%
100 usec 25%
200 usec 6%
300 usec 1.5%
400 usec <0.4%, call it 0

if we assume my previous 500 v (way too high) across a 1000 Ohm person
Ipeak= 500/1000 = 500 mA
from above it decays from 500 to 0 in 400 usec or 0.4 msec
essentially the duration
the peak is 500 but decays rapidly, avg is close to 200 (don't feel like integrating lol)
we'll use 300 mA to be conservative
For 0.4 msec

Dalziels equation for fibrillation
i mA = 175 (avg man) / sqrt(t sec)
or time = (175/300)^2 = 0.34 sec is survivable <<< 0.0004 sec
factor of 85

how much current can be survived per Dalziel in 0.0004 sec?
equation likely not valid at this small a time, but should give an order of magnitude
8750 mA (the person would never see that much) factor of 30
fibrillation would be the least of his worries
P = 8.75^2 x 1000 = 76 kw or 100 hp
v required = 8.75 x 1000 = 8750 v, not happening with lightening

now much depends on how well coupled to earth, golf spikes vs tennis shoes, etc
this will dampen the surge, lower peak and longer decay rate

it does not surprise me a high % survive
Click to expand...

100% correct in terms of ohm's law, but my ignorance wants to inquire. Doesn't lighting also have a series L (reactance) component which effects the amount of I which flows through a given resistance?
 
Lmeagles36 said:
I understand either my logic or math is way off but I don't see where or how, otherwise people wouldn't have a 90 some % rate of surviving a lightning strike.
Bring on the education please!!! Thanks.
Click to expand...

here... let me cloud a logical discussion with alternate facts..... :p

timing of the shock seems to play a factor in lethality. as the heart
is resting a fair bit of the time, between pumping activities, it's control
circuits aren't as likely to fibrillate when they aren't in control mode.

as is the path of the current. and it seems there is a fickle factor
with shock that defies description. current flow is what triggers
fibrillation, and 1/20th of an amp is a lethal threshold. i personally pulled
enough current arm to arm to trip a 20 amp breaker with a four amp
existing load on it, so in theory, i pulled 16 amps. over 300 times the
lethal level.

and i'm still here annoying y'all.

so the definitive answer to your question is that it wasn't those folks
time yet. it wasn't mine either. i've had enough darwin candidate incidents,
both random, and part of faulty logical constructs, to make me grateful for
being alive today.

have a happy 4th of july folks. try not to exterminate yourselves, ok?
 
Fulthrotl said:
i personally pulled
enough current arm to arm to trip a 20 amp breaker with a four amp
existing load on it, so in theory, i pulled 16 amps. over 300 times the
lethal level.

and i'm still here annoying y'all.
Click to expand...

I have seen plenty of 20 Amp breakers carry 25-26 amps for 10 minutes or more before tripping.

Do you go around humming the Armor hot dog song a lot these days? Or other side effects?
 
To trip a 20 A cb you need > 20
the resistance range for a person is 700-1500
there are iso charts for various paths, contact area, voltages, moisture, etc
if we use the lowest of 700 the voltage required to drive say 25 A is
700 x 25 = 17.5 kV
 
growler said:
I have seen plenty of 20 Amp breakers carry 25-26 amps for 10 minutes or more before tripping.

Do you go around humming the Armor hot dog song a lot these days? Or other side effects?
Click to expand...


i've seen that as well.

the breaker tripped, and i have no explanation other than i support it's
behavior wholeheartedly.

honestly, i lead a charmed life.

september of 2011, there was a car behind me, who honked for me to pull
forward, as there was a gap in traffic that i could move forward a carlength
or so.

so i did. it was a red light. what did she think she was going to accomplish?
quite a bit. she saved my life. the tree fell on her. freak accident. killed her.

tn-tn-dpt-tree-4.jpg.jpg

http://www.latimes.com/tn-dpt-0916-tree-20110915-story.html

i was the car in front. happened less than a minute after i moved.
 
Fulthrotl said:
september of 2011, there was a car behind me, who honked for me to pull
forward, as there was a gap in traffic that i could move forward a carlength
or so.

so i did. it was a red light. what did she think she was going to accomplish?
quite a bit. she saved my life. the tree fell on her. freak accident. Killed her.
Click to expand...


I hate to admit it but maybe there is a God and he hates those people that blow their horns in traffic as much as I do.

All joking aside it does make you wonder. I lived through a bad accident back in 1978 and so did everyone in the truck but the stange thing is no one was really hurt bad at all considering the damage to the vehicle. I was thrown clear, a distance of about 40 ft from the vehicle into a small stream, in the only place with enough water to soften the landing. I felt like a dart that had just hit a bulls eye. But then again no one was hurt that bad and the vehicle totally destroyed. At the time I thought that if God looks out for drunks, fools and small children then I was good in at least two catagories ( I wasn't a kid ).

I kind of know this guy that got shot in the mouth with a 22 caliber pistol about 4 years ago. The bullet took out part of one of his front teeth and then recocheted off a back tooth and out the other side of his jaw. I didn't see it happen but did see the wounds. This was at point blank range so I would say he was extremely lucky or something.

There are stange things that happen that would be hard to explain.
 
petersonra said:
doesn't matter much how much electricity goes thru the body so much as how much goes thru your heart or other sensitive organ.
Click to expand...
Half true. Electricity passing through the heart or brain can kill promptly, but electricity passing through any other tissue can cause electroporation. (punching holes in cell walls) After being perforated, the ability to maintain electrolyte balance is compromised and the body begins to poison itself. When electroporation is the cause of death, it usually occurs four days after receiving a shock.
 
drcampbell said:
Half true. Electricity passing through the heart or brain can kill promptly, but electricity passing through any other tissue can cause electroporation. (punching holes in cell walls) After being perforated, the ability to maintain electrolyte balance is compromised and the body begins to poison itself. When electroporation is the cause of death, it usually occurs four days after receiving a shock.
Click to expand...

Is that similar to what happens want cells are "cooked" from boiling the water inside them?
 
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